Transition Highly Aggregated ComplexesSoluble Complexes via Polyelectrolyte Exchange Reactions: Kinetics, Structural Changes, and Mechanism

Abstract

The dissolution of highly aggregated polyelectrolyte complex particles formed in water after addition of salt was studied. The dissolution of aggregates proceeded to soluble complexes on the molecular level of the long-chain component. The driving force of the process is the polyelectrolyte exchange reaction between the aggregates and the free long chains in excess. The kinetics of the process was studied by different light scattering techniques. The rate of dissolution showed a strong dependence on the salt concentration in the solution and on the concentration of the species. The dependence on concentration of the species in solution weakened with increasing salt concentration. Investigations of the structural changes during the dissolution process revealed the presence of only two generations of particles in solution: aggregates and soluble complexes. While the scattering intensity decreased strongly, the dimensions of the aggregates changed only slightly during dissolution, indicating a spontaneous disaggregation of the particles. A mechanism of the dissolution process was proposed, which is in agreement with the experimental findings and previous results in the literature. The process represents a two-step reaction: The first step consists of the release of the short-chain component from the aggregates by an exchange reaction via the free long-chain component in solution (second-order reaction). The second step is the destruction of the aggregates by increasing osmotic pressure in the particle (first-order reaction). The dissolution process may be understood as a model process for the release of DNA from polyelectrolyte complexes in gene therapy.